Adhesive to attach a cooling device to a thermal interface

ABSTRACT

A method of providing thermal connection between a thermal cooling device and an integrated circuit package is provided. An adhesive is applied to a thermal interface outside a heat transfer area thereof. The thermal interface is attached to the cooling device. The device to be cooled is attached to the thermal interface.

BACKGROUND OF THE INVENTION

[0001] (1) Field of the Invention

[0002] The present invention relates to the field of cooling electroniccomponents and circuits. More specifically, the present inventionrelates to attaching electronic components to cooling devices.

[0003] (2) Description of the Related Art

[0004] Cooling devices such as heat sinks or thermal plates are used inconjunction with electronic and microelectronic circuits/components forcooling these circuits/components. Generally, integrated circuitpackages may be cooled by attaching these packages to heat sinks,thermal plates, or other such cooling devices. Heat sinks or thermalplates dissipate the heat generated by the attached integrated circuitpackages during the operation of these circuits. To provide optimal heattransfer, heat sinks or thermal plates are designed to have, generally,a large surface area. A surface area, herein refers to any area of theheat sink or thermal plate in contact with a cooling fluid such as air.The size of the surface area may generally determine the heatdissipating capacity of a heat sink or thermal plate.

[0005] Typically, heat sinks have a plurality of fins upwardly extendingfrom the base plate. The fins conduct heat from the base plate. Heat isdissipated by a cooling fluid, such as air, flowing through spaceslocated between the fins. Typically, a cooling space defined by the finsis defined by the base plate and the vertical surfaces of two adjacentfins. The cooling fluid flows through the cooling spaces, thereby makingcontact with the fins, removing the heat by thermal dissipation(convection) from the fins, and further driving the dissipated heatoutside the heat sink. Most heat sinks or thermal plates, are attachedto the device to be cooled by way of a base plate. The larger the baseplate the more efficient is the heat transfer between the device to becooled (integrated circuit package) and the cooling device (heat sink orthermal plate).

[0006] Generally, a thermal interface such as a film/tape attachedbetween the integrated circuit package and a base plate may be used toreduce the thermal resistance between the integrated circuit package andthe heat sink or thermal plate. A thin layer of pressure sensitiveadhesive (PSA) may be applied to the entire thermal interface surface toattach the thermal interface to the heat sink. However, the PSA is not agood thermal conductor.

[0007] It is desirable to provide a way of attaching a thermal interfaceto a cooling device without adding substantial thermal resistancebetween a device to be cooled such as an integrated circuit package anda cooling device such as a heat sink or a thermal place.

SUMMARY OF THE INVENTION

[0008] The present invention provides a method of providing thermalconnection between a cooling device and a device to be cooled. Anadhesive is applied to a thermal interface outside a heat transfer areaof the thermal interface. The thermal interface is attached to thecooling device. The device to be cooled is attached to the thermalinterface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The features, aspects and advantages of the present inventionwill become more fully apparent from the following Detailed Description,appended claims and accompanying drawings in which:

[0010]FIG. 1 illustrates a top view of a thermal interface to which anadhesive is applied according to one embodiment of the presentinvention;

[0011]FIG. 2 illustrates a top view of an alternative embodiment of thethermal interface with an adhesive applied along the entire periphery ofthe thermal interface;

[0012]FIG. 3 illustrates an exploded cross-sectional view through anumber of devices to be assembled together according to one embodimentof the present invention;

[0013]FIG. 4 illustrates a cross-sectional view through a thermalinterface with a pressure sensitive adhesive (PSA) pattern attached tothe thermal interface near the edges of the thermal interface;

[0014]FIG. 5 illustrates a cross-sectional view through a heat sink towhich the thermal interface, with the PSA pattern applied near the edgesof the thermal interface, is attached;

[0015]FIG. 6 illustrates an integrated circuit package attached to theassembly of the heat sink and thermal interface with the PSA appliednear the edges of the thermal interface;

[0016]FIG. 7 illustrates an integrated circuit package attached to theassembly of a thermal plate and thermal interface with the PSA appliednear the edges of the thermal interface; and

[0017]FIG. 8 illustrates a flow chart diagram of a method of providingthermal connection between a cooling device and a device to be cooledaccording to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0018] In the following description, numerous specific details are setforth to provide a thorough understanding of the present invention.However, one having ordinary skill in the art should recognize that theinvention may be practiced without these specific details. In someinstances, well-known elements, structures, and techniques have not beenshown in detail to avoid obscuring the present invention.

[0019] The present invention provides a method of providing thermalconnection between a cooling device and a device to be cooled. Anadhesive is applied to a thermal interface outside a heat transfer areaof the thermal interface. The thermal interface is attached to thecooling device. The device to be cooled is attached to the thermalinterface. The embodiment of the present invention avoids utilizing PSAon the entire thermal interface surface. Using PSA on the entire thermalinterface surface would be equivalent to adding in an insulating layer.This would significantly increase the overall thermal resistance betweenthe device to be cooled such as an integrated circuit package and acooling device such as a heat sink or thermal plate. By applying anadhesive outside the heat transfer area of the thermal interface, theembodiment of the method of the present invention contributes toproviding thermal connection between the cooling device and the deviceto be cooled without obstructing a heat transfer area of the thermalinterface.

[0020]FIG. 1 illustrates a thermal interface 102 to which an adhesivepattern (hereinafter referred to as “adhesive”) 104 is applied. In oneembodiment according to the present invention, adhesive 104 is apressure sensitive adhesive (PSA) but the present invention is notlimited in scope to a pressure sensitive adhesive implementation ofadhesive 104. Also in one embodiment of the present invention describedherein the PSA 104 is applied alongside two edges 108 of thermalinterface 102. The two strips of PSA 104 have a thickness in a range ofapproximately 0.0125 to 0.025 mm. Thermal interface 102 may be made ofmaterials including silicone, elastomeric materials, or phase-changematerials. One example of a thermal interface material is Chomerics T443film manufactured by Parker Hannifin Corp., Chomerics Division, locatedat 77 Dragon Court, Woburn, Mass. 01888.

[0021] The PSA is applied to the periphery of the thermal interface 102so that a heat transfer area or contact area 106 (shown in dotted lines)remains exposed. Proper transfer of heat is thus allowed through thethermal interface between a device to be cooled such as an integratedcircuit package, for example, and a cooling device, such as a heat sinkor a thermal plate, for example. The integrated circuit package and thethermal plate are later attached to thermal interface 102. Heat transferarea 106 is equal to or larger than a contact area of the integratedcircuit package that is later attached to the thermal interface.

[0022]FIG. 2 shows an alternative embodiment of thermal interface 102 ofthe present invention. PSA pattern 104 is applied along the entireperiphery (4 edges 108) of thermal interface 102.

[0023]FIG. 3 illustrates an exploded cross-sectional view of an assemblyincluding an integrated circuit package 116, thermal interface 102, PSA104 and a heat sink 118. Thermal interface 102 has a first surface 130to which the integrated circuit package 116 is later attached and asecond surface 132 to which PSA 104 is later attached.

[0024]FIG. 4 illustrates an adhesive, such as PSA 104, applied tosurface 132 of thermal interface 102 which is interfacing betweenintegrated circuit package 116 and a cooling device. The cooling devicemay be a heat sink (as illustrated in the figure), or any other coolingdevices such as thermal plates, heat pipes, thermoelectric coolers,water-cooled metal plates, etc.

[0025] Two strips of PSA 104 are applied to the thermal interface 102near edges 108 of thermal interface 102. The strips of PSA 104 areattached outside heat transfer area 106 defined by vertical dotted lines114 and 112, so that the heat emanated from integrated circuit package116 is efficiently transferred by thermal interface 102 to base plate120 of heat sink 118.

[0026] Next, thermal interface 102, with PSA strips 104 applied nearedges 118 thereof, is attached to a surface 140 of base plate 120 asillustrated in FIG. 5. The attachment is mainly due to an adhesivesurface of PSA 104 that makes contact with surface 140 of base plate120. Note that PSA 104 is compliable, becoming very thin when thermalinterface 102 is pressed and attached to base plate 120 of heat sink118. Heat may be transferred from the integrated circuit package 116 tothe heat sink 118 mainly via heat transfer area 106, demarcated bydotted lines 112 and 114. Heat transfer area 106 is not covered by PSA104. The vendor of the heat sink may then ship the assembly, includingthe heat sink 118 with the thermal interface 102 attached thereto, tothe manufacturer of the integrated circuit package, for furtherassembling the integrated circuit package 116 to the assembly.

[0027]FIG. 6 illustrates an integrated circuit package 116 attached tothe assembly of a heat sink 118 and of thermal interface 102 attached tothe heat sink by way of PSA 104. Integrated circuit package 116 may beattached to the thermal interface 102 by way of screw(s) and/or clip(s)(not shown). Arrows 126 indicate the flow of heat from integratedcircuit package 116 to heat sink 118.

[0028]FIG. 7 illustrates an integrated circuit package attached to theassembly of a thermal plate 119 and of thermal interface 102. Thethermal interface 102 has the PSA 104 applied near the edges of thethermal interface.

[0029]FIG. 8 illustrates a flow chart diagram of a method of providingthermal connection between a cooling device and a device to be cooledaccording to one embodiment of the present invention. The method startsat block 802 from where it passes to block 804. At block 804 an adhesiveis applied to a thermal interface outside a heat transfer area of thethermal interface. The method then flows to block 806 where the thermalinterface is attached to a cooling device. Next the method flows toblock 808 where the device to be cooled is attached to the thermalinterface.

[0030] In the foregoing specification, the invention has been describedwith reference to specific embodiments thereof. It will however beevident that various modifications and changes can be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarding in an illustrative rather than arestrictive sense. Therefore, the scope of the invention should belimited by the appended claims.

1. A method of providing thermal connection between a cooling device anda device to be cooled, the method comprising: a. applying an adhesive toa thermal interface outside a heat transfer area of the thermalinterface; b. attaching the thermal interface to the cooling device; andc. attaching the device to be cooled to the thermal interface.
 2. Themethod of claim 1 wherein said adhesive includes a pressure sensitiveadhesive (PSA).
 3. The method of claim 1 wherein said cooling deviceincludes a heat sink device.
 4. The method of claim 1 wherein saidcooling device includes a thermal plate.
 5. The method of claim 1wherein said device to be cooled includes an integrated circuit package.6. The method of claim 1 wherein said adhesive is applied at a peripheryof said thermal interface.
 7. The method of claim 1 wherein said thermalinterface includes a Chomerics T443 film.
 8. An apparatus to providethermal connection between a cooling device and a device to be cooled,the apparatus comprising: a thermal interface that includes a heattransfer area; an adhesive applied to the thermal interface outside theheat transfer area; and a cooling device to which the thermal interfaceis attached.
 9. The apparatus of claim 8 wherein said adhesive includesa pressure sensitive adhesive (PSA).
 10. The apparatus of claim 8wherein said cooling device includes a heat sink.
 11. The apparatus ofclaim 8 wherein said cooling device includes a thermal plate.
 12. Theapparatus of claim 8 wherein said device to be cooled includes anintegrated circuit package.
 13. The apparatus of claim 8 wherein saidadhesive is applied at a periphery of said cooling device.
 14. Theapparatus of claim 8 wherein said thermal interface includes a ChomericsT443 film.
 15. An apparatus comprising: a thermal interface thatincludes a first surface with a heat transfer area and a second surface;an adhesive applied to the first surface outside the heat transfer area;a cooling device attached to the thermal interface at said first surfacethereof; and a device to be cooled attached at said second surface ofthe thermal interface.
 16. The apparatus of claim 15 wherein saidadhesive includes a pressure sensitive adhesive (PSA).
 17. The apparatusof claim 15 wherein said cooling device includes a heat sink.
 18. Theapparatus of claim 15 wherein said device to be cooled includes anintegrated circuit package.
 19. The apparatus of claim 15 wherein saiddevice to be cooled includes a thermal plate.